Explosives
Several different types of explosives were used in the blasts. They differ primarily in their speed of detonation.
A slow explosive, similar to a ditching dynamite is used where a lot of push is needed. These generate the push by producing large amounts of gaseous byproduct which acts to push material ahead of it. A common example is in ditching work, where you want to move material from a ditch up onto the banks surrounding it.
A fast explosive is used where a shattering effect is needed to rip apart massive concrete structures. In this case you want to shatter the concrete but not blow it all over the place. Another application is in cutting steel beams. Again, you want to cut it but not sent huge shrapnel pieces flying.
A mid range explosive has a good mixture of shattering ability along with reasonable push characteristics. This type finds great use in shooting certain pillars where it is necessary to both shatter the pillar and rapidly remove the pillar material from its position to allow material above it to drop into it's place.
An analogy to the different types might be as follows: A slow type might be when two sumo wrestlers push you off your feet, a fast type would involve an extreme slap to the face, and a mid range type would involve a good slap to the face and then a firm shove. They each have their place in dropping an elevator.
What is slow for an explosive? Forget about outrunning a slow explosive. Slow means about 14,000 feet/second. Mid range is around 18,000 feet/second while a fast one detonates at 25,000 feet/second. If my math is right, the space shuttle could outrun the slow and medium types but not the fast explosive. (with particle ejection velocities from a blast in the range of 6,000 feet/sec I suppose it is possible that Luke Skywalker actually could have made it out safely from the Death Star once he got up to speed.)
In ripping apart concrete with explosives, apparently only a small amount of concrete is actually crushed by the compression of the explosion itself. This compressive failure is concentrated within only the first several inches away from the explosive. Most of the blast damage is done by the trailing edge of the shock wave where the concrete is actually pulled apart under tension. Further out, larger pieces are torn loose by simple tensile failure due to the disintegration of the pillar itself. In the areas excavated after the blasts, nothing was found of any of the pillars in pieces larger than several inches. Click on the picture below to see what is left of a solid 4' diameter pillar in the "C" head house. This was a non-critical pillar that was a test shot. Notice the amount of reinforcing steel.
